Goerz "Mollarlinse"

[Uli Mayer]

In various books I found descriptions of a "Mollarlinse" that should like an thick ordinary clear filter but which in fact is a doublet: a plano-convex lens and a plano-concave lens having their curved surfaces cemented together. Invented by Franz Weidert and made by Goerz this "Mollarlinse" ( its German brand name, maybe there were others abroad) was to be used as a supplementary lens that - while keeping main image focus unchanged - introduced enough chromatic aberration to soften the image and to broaden depth of field. (for details, please see U.S. pat. 1,556,982; 1925)

Has anyone ever actually seen this "device" and could anyone tell about his/her practical experience with it?

Thanks
Uli

[Dan Fromm]

Uli, this is also a way of making a variable density center filter for, e.g., wide angle lenses. Suggest a search for apodization, apodizing.

Cheers,

Dan

[Uli Mayer]

Thanks for your quick answer, Dan.

I must admit I have never heard about this "apodization" or "apodizing" before , and worse, understanding it is quite a task. But I'll try hard.
My first impression after some reading may be wrong, but I think the "Mollarlinse" does the opposite of apodizing. It's not removing aberrations but enhancing one of them, by selectively adding secondary color (chromatizing). And it does so - this is the most fascinating thing to me - without touching the central part of the photographically usable spectrum. A smart approach - and maybe as effective as when using an Imagon, which does it in a different way and is certainly more costly.

Weidert's patent includes the full lens description, thus providing a good basis for trying to build one's own. (However, finding single lenses of at least similar specs, plus cementing both to a flat may prove difficult.) My question is: Is it worthwhile? Without first learning about practical experience with an original Mollar lens I would not try.

[Ernest Purdum]

Most efforts at softening definition since the 1880's or so have been based on adding spherical aberration rather than chromatic. Weidert apparently had his own thoughts on the subject since his patent date was 1925. Maybe he had something special in mind, but I think staying with the majority method would be more likely to produce desired results or at least to be easier to work with.

As Dan pointed out, the construction is similar to that of a center filter, the difference being that in the Mollarlinse both pieces of glass would be clear, rather than the neutral density of the plano-convex element of the center filter. Center filters are very expensive, and I think the principal reason is that they are very hard to make because of their extreme thinness. If the Mollarlinse elements are thicker, they would be somewhat easier to make but I suspect they woiuld still be difficult.

[Uli Mayer]

Ernest,
it's a thick lens, 4.6mm to be precise.
(http://www.google.com/patents?vid=USPAT1556982&id=wilCAAAAEBAJ&dq=1556982)

If there weren't highly-respected authors (Harting, Flügge, Merté, David and probaby others, too ) who wrote about the optical idea behind the Mollarlinse - actually sacricing many or even more lines to this soft-focus lens than to others - I wouldn't give a DIY project any second thought.

I do not know why and when the Mollarlinse disappeared from the Goerz list. But I doubt, it vanished of purely optical reasons or because of the costs to make it. (Even if the glass types to be used had been expensive, the whole thing should have been much cheaper than to produce let's say: an Imagon !) Around the time it was made (early twenties) there was the take-over of Goerz by Zeiss. Maybe Zeiss had already something else (something better?) to offer and wanted to get rid of a competing device.